1. Field of the Invention
The present invention is in the field of catalysts for use in upgrading heavy oil feedstocks into lower boiling, higher quality materials. More particularly, the invention relates to thermally stable catalyst precursors containing molybdenum salts that can be mixed with heavy oil feedstocks to form a hydroprocessing catalyst in situ within heavy oil.
2. Related Technology
World demand for refined fossil fuels is ever-increasing and will eventually outstrip the supply of high quality crude oil. As the shortage of high quality crude oil increases there is increasing demand to find ways to better utilize lower quality feedstocks and extract fuel values from them.
Lower quality feedstocks are characterized as including relatively high quantities of hydrocarbons having a boiling point of 524° C. (975° F.) or higher. They also contain relatively high concentrations of sulfur, nitrogen and/or metals. High boiling fractions typically have a high molecular weight and/or low hydrogen/carbon ratio, an example of which is a class of complex compounds collectively referred to as “asphaltenes”. Asphaltenes are difficult to process and commonly cause fouling of conventional catalysts and hydroprocessing equipment (e.g., through formation of coke and sediment).
Examples of lower quality feedstocks that contain relatively high concentrations of asphaltenes, sulfur, nitrogen and metals include heavy crude and oil sands bitumen, as well as bottom of the barrel and residuum left over from conventional refinery process (collectively “heavy oil”). The terms “bottom of the barrel” and “residuum” (or “resid”) typically refer to atmospheric tower bottoms, which have a boiling point of at least 343° C. (650° F.), or vacuum tower bottoms, which have a boiling point of at least 524° C. (975° F.). The terms “resid pitch” and “vacuum residue” are commonly used to refer to fractions that have a boiling point of 524° C. (975° F.) or greater.
Converting heavy oil into useful end products requires extensive processing, including reducing the boiling point of the heavy oil, increasing the hydrogen-to-carbon ratio, and removing impurities such as metals, sulfur, nitrogen and carbon forming compounds.
When used with heavy oil, existing commercial catalytic hydrocracking processes easily become fouled or rapidly undergo catalyst deactivation due to sintering and coking. The undesirable reactions and fouling involved in hydrocracking heavy oil greatly increases the catalyst material and maintenance costs of processing heavy oils, making current catalysts unsuitable for hydroprocessing heavy oil.
U.S. Pat. No. 5,578,197 to Cyr et al. discloses an effective technology for hydroprocessing heavy oils using a hydrocarbon-soluble molybdenum salt that decomposes in the heavy oil during hydroprocessing to form, in situ, a hydroprocessing catalyst, namely molybdenum sulfide. Once formed in situ, the molybdenum sulfide catalyst is highly effective at breaking up asphaltenes and other complicated hydrocarbons while preventing fouling and coking.
A significant problem with commercializing oil soluble molybdenum catalysts such as the one in Cyr et al. is the cost of the catalyst. Even small improvements in catalyst performance can have a significant benefit to the cost of the hydrocracking process due to the increase in output and/or the reduced use of the catalyst.
The performance of oil soluble molybdenum catalysts depends significantly on the concentration of the catalyst metal in the heavy oil and on how well the catalyst precursor can be dispersed within the heavy oil. U.S. Pat. No. 7,670,984 to Wu et al, incorporated herein by reference, discloses molybdenum based compounds used as a catalyst precursor (hereafter referred to as the “'984 patent catalyst precursor”) that can increase the percent of metal in the catalyst while maintaining or improving solubility in heavy oil, leading to improved efficiency of processes for hydrocracking heavy oils using oil soluble molybdenum catalyst precursor compounds.